The invention relates to dental adhesive primers. In particular, the invention provides a self-etching dental adhesive primer composition and polymerizable surfactants. The primer composition is used in a method of coating a water insoluble polymerizable monomer mixture on a tooth or bone substance. The primer composition is useful as an adhesive or adhesion promoter to affix dental filling materials or bone cements to tooth material. Other uses include forming a protective film on the tooth or bone, or for fixing bone cements in position. The composition essentially comprises an emulsion of water immiscible polymerizable monomers, oligomers and adhesion promoters in water. By using an emulsion of the polymerizable substances in water the need for volatile organic solvents is avoided and biocompatability is enhanced. A further advantage is that independent of the resin phase, the pH of the aqueous phase can be adjusted to provide a self-etching action on the tooth and bone substance, thus enhancing adhesion of the layer to the tooth or bone without requiring a separate etching step. The composition preferably further comprises initiators, accelerators, and inhibitors as often used in unsaturated polymerizable mixtures. Further, the composition preferably comprises surfactants and colloidal silica particles to aid in the formulation of an emulsion and to help keep this stable. Optionally, fluoride releasing agents, bactericidal substances or medicinally beneficial materials may also be included in either aqueous or the resin phase of the composition. The emulsion will typically contain droplets with diameters of less than 30 microns of the polymerizable monomers, oligomers and adhesion promoters. More preferably most of the droplets have a diameter less than 10 microns. Preferably a portion of the droplets will have a diameter less than 1 micron. On applying the composition to the tooth or bone substance the film may first be left for a few seconds to allow an etching action to occur. The water may then be gently blown away, whereby the droplets of polymerizable monomers, oligomers and adhesion promoters coalesce to form a continuous film. No washing of the treated surface is required.
The present invention provides surfactants containing polymerizable monomers for use in compositions. The surfactants are able to polymerize into the matrix to become part of the polymer, and are thereby immobilised. Applications for surfactants containing polymerizable monomers are wide and varied, and include for instance paints and coatings, inks, and glues, particularly those where the coating, ink, or glue is cured by exposure to light. In particular, the surfactants of the present invention are useful in dental restorative materials.
Prior art water-soluble hydrophilic materials form very weak spongy polymers, and have undesirable physical characteristics in the cured film layer. The polymerizable resin mixtures and composites used for the repair and replacement of tooth substance, or for the fixation of prosthesis into bone do not adhere of themselves to the tooth or bone substance, and some means is needed to keep them in place. This has long been a problem, and various methods have been developed to overcome it. Initially the attachment method was purely mechanical, and in dental practice large volumes of tooth had to be drilled away to provide sufficient anchorage to keep the filling material in place. U.S. Pat. No. 4,514,342 discloses adhesion promoters such as PENTA. U.S. Pat. No. 5,645,429 discloses primer and adhesive combined into one formulation. Although this has excellent adhesion to dentin, adhesion to unetched enamel is lower than when the enamel is first etched. Therefore when the highest adhesion to both dentin and enamel is required the enamel still needs to be etched, and the steps needed to produce an adhering tooth filling material are first etching, next applying the combined primer/adhesive, and finally applying the filling material. Although this is a considerable improvement over two component adhesives, it still requires considerable time and skill on the part of the dentist. After the tooth material has been etched, for instance, it has to be totally protected from contamination with body fluids. If contamination does occur, then the etching procedure has to be repeated. It would therefore be a further advantage if the etching procedure could be combined with the application of the adhesive, since this would not only save the dentists time, but would also eliminate one of the steps in which contamination of the prepared surface is possible. This would in consequence lead to a further improvement in the quality and reliability of the completed restoration of the tooth. These problems of prior art dental primer/adhesive are overcome by the composition, method and product of the present invention.
Surfactants are used in a wide range of purposes, often to help liquids to spread out over a surface, or to help otherwise incompatible components to mix and remain as a homogenous formulation. Often, a surfactant has to do both simultaneously. A common example is washing-up liquid, which enables water to spread out on a greasy surface, and also helps to keep the loosened globules of fat suspended in the water. There are many types of surfactant, but all consist basically of a hydrophobic part and a hydrophilic part. Both the hydrophobic and hydrophilic parts can comprise either a long chain, or a compact xe2x80x9cheadxe2x80x9d. In addition, the hydrophilic part can be either ionic or non-ionic. There are many possible ways of combining these different hydrophobic and hydrophilic parts, leading to a wide range of possible surfactants. Another common use of surfactants is in cosmetic creams and medicaments, where they are used to keep for instance paraffin oil or other water insoluble materials suspended in an aqueous base. This type of formulation is also known as an oil in water emulsion. By suitable choice of surfactant it is also possible to keep droplets of water suspended and stable in a non water miscible oil, and this is known as a water in oil emulsion. Surfactants are also often used in paints, glues, and other surface coatings, and sometimes two or more surfactants are used together to provide optimum surface wetting properties as well as optimum emulsion stability. With a paint, or other coating that is intended to dry, it is usually desirable that when the coating is dry, the surfactant is de-activated or immobilised in some way. In the case of coatings, leaching of the surfactant or its migration towards the airxe2x80x94coating interface can produce discoloration, whereas migration and concentration at the hard surface to which the paint or coating is attached can cause the coating to come loose from the surface to which it is adhering. In essence a surfactant is a material which contains both a non polar hydrophobic end and a polar hydrophilic end, and which is able to form an interface between two surfaces of differing polarity. The word xe2x80x9csurfacesxe2x80x9d is used broadly when applied to surfactants, and can mean either two solid surfaces, two liquid surfaces, or one solid and one liquid surface. However, not all materials which have both polar and non-polar ends are effective surfactants. The non polar end, for instance has to be large enough to keep it firmly attached to a non polar solid surface, or to keep it directed towards or within the surface of a non polar liquid surface. Likewise, the polar end has to be large enough to keep it within the polar environment. The ratio of the polarity of the hydrophilic end to the non polarity of the hydrophobic end also has to be correct and ideally should be optimised for each application. Because it is often hard to find one single surfactant with the ideal properties, mixtures of two or more surfactants are often used in practical formulations. The polarxe2x80x94nonpolar properties of the surfactants are approximately additive, and by choice of a suitable ratio of suitable surfactants a wide range of applications can be covered. Many successful surfactants are known, for instance those known as the Spans, which consist of esters of long chain fatty acids with sorbitan. By changing the length of the fatty acid and the number attached to the sorbitan group, a range of surfactants with varying properties is obtained. Another group of commonly used surfactants are those known as the Tweens. These also consist of esters of fatty acids with sorbitan, but with the addition of a polyethylenoxide chain attached to the sorbitan. By changing the length and number of the fatty acids and also the length of the polyethylenoxide chain, a further range of surfactants is produced. Yet a further group of surfactants comprises esters of fatty acids directly with polyethylenoxide. By varying both the fatty acid and the length of the polyethylenoxide chain surfactants with varying properties can be produced. The surfactants described above all come within the general group known as nonxe2x80x94ionic surfactants. However, surfactants may also be produced by combining non-polar groups with polar ionic groups such as phosphates, sulfates, quaternary amines, and carboxylic groups. A well known example of this class is sodium lauryl sulphate. However, none of the above surfactants contains an easily polymerizable group which would enable it to be incorporated permanently into the matrix of which it is part. Water dispersible polyurethanes containing polyalkylene oxide polyether chains and sulfonate groups are already know, as illustrated in U.S. Pat. No. 4,190,566, U.S. Pat. No. 4,303,774, and U.S. Pat. No. 5,624,758. However these materials do not contain unsaturated polymerizable groups, and are not polymerizable.
It is an object of the present invention to provide a composition and method for simultaneously etching a tooth or bone surface and deposition of a polymerizable priming resin layer thereon.
It is an object of the invention to provide a self etching adhesive dental primer composition, comprising water, surfactant and polymerizable material in suspension in said water, the polymerizable material comprising monomers, which are water immiscible.
It is an object of the invention to provide a method for coating a tooth comprising forming an emulsion of droplets of water immiscible monomers in water by high shear mixing for at least 5 minutes, applying the emulsion to a surface of a tooth in a patient""s mouth and evaporating the water.
It is an object of the invention to provide a dental product formed by providing a self etching adhesive dental primer composition, comprising water, surfactant and polymerizable material in suspension in the water, the polymerizable material comprising monomers which are water immiscible. Preferably at least a portion of the monomers having a moiety selected from the group consisting of phosphoryl and a salt of phosphoryl, the monomers having an average molecular weight less than 1000. The primer is applied to unetched enamel of a dental tooth and polymerizing the polymerizable material to form a dental product having adhesion to the enamel of more than 13 MPa.
It is an object of the invention to provide a compound within the scope of general formula: (R)axe2x80x94Lxe2x80x2xe2x80x94[R1]xe2x80x94Lxe2x80x3xe2x80x94{X}b, wherein R represents a polymerizable moiety, R1 is a hydrophobic hydrocarbon moiety, X is an ether group, a and b each independently is an integer from 1 to 50, Lxe2x80x2 is a linking group capable of linking R to R1, Lxe2x80x3 is a linking group capable of linking R1 to X and neither Lxe2x80x2 nor Lxe2x80x3 is a carbon to carbon bond or an ether group.
High shear mixing typically uses a mixing blade rotated adjacent to a stationary plate with small holes therethrough. As referred to herein the rotating blade of the high shear mixer is rotated at about 22,000 revolutions per minute in a container having a volume of about 500 ml. High shear mixing to form compositions in accordance with the invention is preferably for at least 1 minute, more preferably for at least 3 minutes and most preferably for about 5 minutes.
As used herein xe2x80x9cPENTAxe2x80x9d refers to dipentaerythritolpentacrylate phosphoric acid ester, prepared according to Example 2 of U.S. Pat. No. 4,816,495.
For convenience and easy reference herein, the various surfactants have been given a code such as G750, whereby G stands for glycerol dimethacrylate, and 750 is the mean molecular weight of the polyethyleneglycol chain moiety used.
As used herein BHT refers to 2,6-di-tert-butyl-4-methyl phenol.
As used herein FTIR refers to Fourierxe2x80x94Transform Infra red Spectroscopy.
The invention provides a self etching adhesive dental primer composition, a method of use of the primer composition and a product formed from the primer. The dental product is formed from the primer composition which includes water, surfactant and polymerizable material in suspension in the water. The polymerizable material includes monomers which are water immiscible. Preferably at least a portion of the monomers have a moiety selected from the group consisting of phosphoryl and a salt of phosphoryl. The monomers have an average molecular weight less than 1000. The primer is used by applying to unetched dental tooth enamel and the polymerizable material is polymerized to form a dental product having adhesion to the enamel of more than 13 MPa.
The invention provides polymerizable surfactant compounds within the scope of general formula:
(R)axe2x80x94Lxe2x80x2xe2x80x94[R1]xe2x80x94Lxe2x80x3xe2x80x94{X}b
wherein R represents a polymerizable moiety,
R1 is a hydrophobic hydrocarbon moiety,
X is an ether group,
a and b each independently is an integer of 1, or more and
Lxe2x80x2 is a linking group capable of linking, R to R1 
Lxe2x80x3 is a linking group capable of linking R1 to X and neither Lxe2x80x2 nor Lxe2x80x3 is a carbon to carbon bond.
Previous attempts to produce polymerizable aqueous formulations have all involved water-soluble monomers and polymers. It has now been found possible to produce stable suspensions of water immiscible monomers in water, in which the insoluble monomers are present as tiny, separate droplets suspended in water. The size of the largest dimension of each droplet of resin in the suspension is preferably less than 30 microns and more preferably less than about 10 microns. Such a suspension of a water immiscible component in water is generally referred to as an oil-in-water emulsion. Preferably, one or more surfactants or other surface active agents are added either singly or in combination to help keep the suspension stable. Because the restriction of water solubility of the resin is removed, the wide range of monomers commonly used in dentistry can be employed in the present invention, and the physical characteristics of the cured resin layer can adjusted or optimized without restriction. The pH of the aqueous phase can be adjusted independently of the resin phase as required.
A wide range of ethenically unsaturated monomers, polymerization initiators, and surfactants are useful in compositions in accordance with the invention.
Human extracted teeth without significant anatomical alterations, defects or restorations were cleaned and disinfected by soaking in 1% sodium hypochlorite solution for 18 to 24 hours, rinsed, and then stored at from 1 to 8xc2x0 C. in 1% sodium chloride I water (saline solution) until used within six months.
Teeth were prepared for adhesion to dentin by hand sanding them using wet 300 grit silicon carbide paper, to expose an area of dentin at a plane just below the original interface between the enamel and the dentin. This area was then polished by hand sanding with wet 600 grit silicon carbide paper. The teeth were kept in water until used within 1 to 12 hours.
When adhesion to enamel was to be tested, the teeth were chosen so that an approximately flat area of enamel about 5 mm in diameter was present. This area was washed and cleaned using wet 1200 grit silicon carbide powder and a bristle brush rotating in a dental handpiece. The teeth were then used within 6 hours as below.
The surface to be adhered to was dried lightly with a paper tissue, and the treatment solution or emulsion applied using a felt applicator as supplied by DENTSPLY for 10 to 30 seconds and then the remaining solvent or water was evaporated by gently blowing with a stream of dry oil free air. The layer of remaining resin was light cured by irradiating it for ten seconds with light from a dental light curing unit having a minimum output of 350 milliwatt/square centimeter in the 500 to 500 nm wavelength range (for instance a Spectrum curing unit sold by DENTSPLY International Inc.). A portion of plastic straw of 5 mm internal diameter and about 4 mm long was placed end on the prepared surface and filled with a light curing dental filling material (Spectrum(trademark) DENTSPLY International Inc.). Finally, the filling material was cured by irradiating for forty seconds from the exposed end with the dental light.
The prepared samples were stored for 24 hours in water at 37xc2x0 C. before being thermocycled 500 times between water baths held at 5xc2x0 C. and 55xc2x0 C. with a dwell time in each bath of 20 seconds. The thermocycled samples were then left in water at 37xc2x0 C. overnight before being tested in shear using a Zwick universal testing machine model Z010 with a cell having a maximum load of 500 Newtons, a crosshead speed of 1 mm per minute and a 2 mm diameter chisel. The chisel has a tip point formed at the lower end by grinding and positioning a planar surface across the end of the cylinder at a 45 degree angle to the central axis of the cylinder. In test position, the tip point of the chisel was applied against the composite. Each tooth was mounted vertically in plaster for the test. A minimum of six samples were prepared for each test, and the mean adhesion was calculated.
In the examples below, Span 80 (manufactured by Atlas Powder Company) is sorbitan monooleate, commercially available from many sources including Adrich, and Tween 80 (manufactured by Atlas Powder Company) is polyoxyethlene(20)-sorbitan monooleate, also available commercially from many sources, including Aldrich.
Surfactants of the present invention have polymerizable groups such as hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycerol dimethacrylate, pentaerythritol triacrylate and the like which have been attached via urethane linkages and a hexyl, cyclohexyl, pentyl, octyl or other hydrocarbon group moiety to polyethylenegycol chains of varying length and numbers. The methacrylate or acrylate moiety (hereafter written as (meth)acrylate) together with the hydrocarbon group moiety form a non polar hydrophobic end, while the polyethyleneglycol chain forms a polar hydrophilic end. By varying the number of (meth)acrylate groups and the length or number of the polyethyleneglycol or chains, surfactants with a wide variety of properties may be produced. In addition to the (meth)acrylate groups, other non polar groups such as fatty acids may also be incorporated to provide an even more hydrophobic end when this is required. The polyethyleneglycol chain may further be broken in several short chains if desired. A common method of determining the suitability of a surfactant for a particular use is to measure or calculate its HLB value. There are several methods to estimate the HLB value of materials, but for surfactants containing polythylenglycol chains, the HLB value is approximately given by the relationship:
HLB is equal to the mole percent of hydrophilic group divided by five.
For materials not containing a polythylenglycol chain or chains the HLB value of a material may be approximately calculated by adding together the so called xe2x80x9cgroup numberxe2x80x9d of the individual chemical groups contained in the compound. In this case the HLB value is approximately given by the relationship:
HLB is equal to seven added to the sum of the hydrophilic groups numbers and the sum of the lipophilic group numbers
These methods are described in, for example, xe2x80x9cSurfactant Systems, D. Atwood and A. T. Florence, published by Chapman and Hallxe2x80x9d. The HLB values given below were calculated by one of these methods, and are meant only as a rough guide to the properties of the surfactants described.
The invention provides polymerizable surfactant compounds within the scope of general formula:
(R)axe2x80x94Lxe2x80x2xe2x80x94[R1]xe2x80x94Lxe2x80x3xe2x80x94{X}b
wherein R represents a polymerizable moiety,
R1 is a hydrophobic hydrocarbon moiety,
X is a ether group,
a and b each independently is an integer of 1, or more and
Lxe2x80x2 is a linking group capable of linking, R to R1 
Lxe2x80x3 is a linking group capable of linking R1 to X and neither Lxe2x80x2 nor Lxe2x80x3 is a carbon to carbon bond.
Use of the polymerizable surfactants as emulsion stabilisers.